1. Field of the Invention
The present invention relates to a disk cartridge and, more particularly, to a disk cartridge having an improved construction for securing a cleaning sheet which is disposed on the inner side of the cartridge case.
2. Description of the Prior Art
A known disk cartridge will be described with specific reference to FIGS. 9 and 10.
The disk cartridge has a cartridge case 1, a sheet-like flexible magnetic disk 2 rotatably disposed in the cartridge case 1, and a cleaning sheet 3 which is fixed to the inner surfaces of both panels of the cartridge case 1. The cleaning sheet 3 is made of, for example, a non-woven cloth of a fiber mixture composed of fibers of rayon and polypropylene, a fiber mixture composed of rayon and polyethylene terephthalate, fibers of polyethylene terephthalate alone, or the like. In manufacturing the disk cartridge, the cleaning sheet 3 is fixed to the inner surface of the cartridge case in a state developed as shown in FIG. 10 by being welded by means of, for example, ultrasonic wave.
FIG. 11 illustrates a method in which the cleaning sheet 3 is fixed to the inner surface of the cartridge case by being welded by means of, for example, ultrasonic wave. The cleaning sheet 3 to be fixed is laid on the inner surface of the cartridge case 1 while an electrode 5 is placed in contact with the other, i.e., outer surface, of the cartridge case 1. Then, a welding pin 15 is pressed into/against the cleaning sheet 3 towards the cartridge case 1 and ultrasonic energy is supplied so as to spot-weld the cleaning sheet 3 onto the cartridge case 1.
The welding is conducted at a multiplicity of spots which are denoted by 12 in FIG. 10. After the completion of fixing of the cleaning sheet 3 to the inner surface of the cartridge case 1, a punching is conducted to form various openings or apertures such as a driving hole 8, a head opening 9 and a detection hole 10, as well as a notch 11. Then, the cartridge case which is still in the development state, is folded along an imaginary line X-X such that two opposing panels are formed and then the envelope flaps 5a and 5c are folded to overlie the opposite panel. Then, the flaps 5a and 5c are fixed by, for example, ultrasonic welding as shown in FIG. 9, thereby forming a sack-like disk cartridge. Meanwhile, the magnetic disk 2 is punched out from a green sheet and is inserted into the sack-like disk cartridge. Subsequently, the remaining flap 5b is folded to lie on the opposing panel and fixed by welding thereto, thus completing the disk cartridge.
This known disk cartridge, however, suffers from the following disadvantage in regard to the fixing of the cleaning sheet and there is an increasing demand for a method for eliminating such a disadvantage.
As a result of the spot welding, the cleaning sheet and the cartridge case are molten at the same time at a multiplicity of spots so as to be fixed together. When the pin 15 is raised after the welding, the molten material of the cartridge case is inevitably raised to form keen edges or burrs 1A which project towards the cleaning sheet 3 as shown in FIG. 12. Obviously, the formation of such burrs 1A is not preferred from the view point of protection of the disk, considering that the disk rotates in contact with the cleaning sheet.
In a conventional general method of producing a disk cartridge, welding spots 12 are uniformly distributed over the entire area of the disk cartridge 1 during the developed state as shown in FIG. 13. In contrast, in another known method as shown in FIG. 14, the welding is conducted along a plurality of parallel lines 20 so as to reduce the number of welding burrs or welding portions, thereby ensuring smooth rotation of the disk received in the disk cartridge.
FIG. 15 shows a still another known method in which there are provided belt-like zones in which the welding spots are distributed in a high density and zones in which there is no welding spot. This arrangement also reduces the area of contact between the disk and the welding burrs or welding portions, thus ensuring a smooth rotation of the disk.
Another problem encountered with the known disk cartridge is that the disk in the disk cartridge tends to be damaged by an external force which is applied to the disk cartridge by a pressing member or a pad which is incorporated in the recording/reproducing apparatus on which the disk cartridge is used.
This problem will be explained in more detail. The magnetic disk 2 in the disk cartridge is thin and is made from a material which is highly flexible. Therefore, when the magnetic disk 2 is driven for the purpose of recording or reproduction, it is a common measure to pinch the disk by pressing the cartridge case from both sides thereof in the regions A and B (see FIG. 9) which are on both sides of the head access opening 9 by means of pads which are provided on the recording and reproducing apparatus, thereby avoiding any error which may otherwise be caused by fluttering of the magnetic disk 2 in the disk cartridge case 1. The pressure applied by the pads increases the possibility for the magnetic disk to contact the welding burrs 1A directly or indirectly through the cleaning sheet, the thickness of which has been reduced at the welding spot. In consequence, problems are caused such as damaging of the disk sur faces resulting in the recording and reproduction are being impaired.